<div id='block-main_menu' class='block block-main_menu'>
    <div class='block-title'></div>
    <div class='block-content'>
        <?php if ($main_menu): ?>
        <?php print theme('links__system_main_menu', array(
          'links' => $main_menu,
          'attributes' => array(
            'id' => 'main-menu-links',
            'class' => array('links', 'clearfix'),
          ),
          'heading' => array(
            'text' => t('Main menu'),
            'level' => 'h2',
            'class' => array('element-invisible'),
          ),
        )); ?>
        <?php endif; ?>
    </div>
</div>
